ROBUST DARK ENERGY CONSTRAINTS FROM SUPERNOVAE, GALAXY CLUSTERING, AND 3 yr WILKINSON MICROWAVE ANISOTROPY PROBE OBSERVATIONS

摘要

Type Ⅰa supernova (SN Ⅰa), galaxy clustering, and cosmic microwave background (CMB) anisotropy data provide complementary constraints on the nature of the dark energy in the universe. We find that the 3 yr Wilkinson Microwave Anisotropy Probe (WMAP) observations give a CMB shift parameter of R ≡ (Ω_mH_0~2)~(1/2)∫_0~(z_(CMB)) dz′/H(z′) = 1.70 ± 0.03. Using this new measured value of the CMB shift parameter, together with the baryon acoustic oscillation (BAO) measurement from the Sloan Digital Sky Survey (SDSS), and SN Ⅰa data from the HST/GOODS program and the first-year Supernova Legacy Survey, we derive model-independent constraints on the dark energy density ρx(z) and the cosmic expansion rate H(z). We also derive constraints on the dark energy equation of state w_X(z) = w_0 + w′z (with cutoff at z = 2) and w_X(a) = w_0 + (1 — a)w_a. We find that current data provide slightly tighter constraints on ρx(z) and H(z) as free functions in redshift and roughly a factor of 2 improvement in constraining w_X(z). A cos-mological constant remains consistent with the data; however, uncertainties remain large for model-independent constraints of dark energy. A significant increase in the number of observed SNe Ⅰa between redshifts of 1 and 2, complemented by improved BAO and weak-lensing cosmography measurements (as expected from the JEDI mission concept for the Joint Dark Energy Mission), will be required to dramatically tighten model-independent dark energy constraints.